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Étude numérique des instabilités dans le procédé de coextrusion des polyesters

Abstract : The polymer coextrusion process is a new method of sheet metal lining. It allows to substitute lacquers for steel protection in food packaging industry. It consists in extruding different polymers in the same die in order to get a multi-layer product which will provide simultaneously adhesion properties (on metal) as well as mechanical and printing properties for the coating. The coextrusion process may exhibit flow instabilities at the interface between the two polymer layers. These instabilities depend on several parameters, e.g. processing temperatures and flow rates, differences in viscosity and elasticity. The objective of this study is to check the influence of processing and rheology parameters on the instabilities. Finite element numerical simulations of the coextrusion process allow to investigate various stable and instable flow configurations. 3D finite element computation of the whole die geometry (with only one polymer) points out that the flow is 2D both at the die entry and at the die exit, which are supposed to initiate the coextrusion defects. 2D dynamic stability analysis of the coextrusion flow points out the development of progressive waves along the die geometry. In the purely viscous case, the driving force is the Reynolds number (which is obviously very small for molten polymer flows) and the initial perturbation vanishes along the die. In the viscoelastic case, the driving force is the Weissenberg number which may be much higher than the Reynolds number. The results show that the amplitude of the progressive waves may increase or decrease, depending on the processing parameters, towards the die exit. The results are compared with experiments carried out by our industrial partner. The simulations predict surprisingly well the experimental results.
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Submitted on : Monday, December 22, 2008 - 10:29:14 AM
Last modification on : Wednesday, October 14, 2020 - 4:02:37 AM
Long-term archiving on: : Tuesday, June 8, 2010 - 6:02:42 PM

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  • HAL Id : tel-00348802, version 1

Citation

Omar Mahdaoui. Étude numérique des instabilités dans le procédé de coextrusion des polyesters. Mécanique [physics.med-ph]. École Nationale Supérieure des Mines de Paris, 2008. Français. ⟨NNT : 2008ENMP1576⟩. ⟨tel-00348802⟩

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